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300tdi revs dropping to 1500rpm


chibiace

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My '95 land rover discovery auto diesel with the 300tdi engine was sitting for afew months and when i got it going again its got this weird issue with the engine.

when you push down the accelerator the revs will go up like normal but will soon drop down to just below 1500rpm and stay there, no matter how far you push the peddle in it wont go any higher

it is possible to get it working steady but only if the peddle is pumped up over 3000rpm

Heres a video showing it:

https://www.youtube.com/watch?v=zdaEkRXyZWM

I have fresh fuel, cleaned the sedimenter, new fuel filter, new lift pump, checked injectors were working correctly, usual exhaust emissions.   

would love to get out driving again as its my kayak wagon, any help greatly appreciated.

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20 hours ago, jason110 said:

Put some diesel in it. I wouldn't trust the fuel gauge. Have you checked the air filter? Is it smoking? Have you had any work done to it recently? Check the intercooler hoses, they might be collapsing under vacuum. 

it's got fresh fuel, first thing I suspected was water in it so I ran it empty and put new stuff in.

checked the air filter and the sensor next to it, looked good.

do all my own work was previously my father vehicle who also did his own work.

I will check the intercooler hoses.

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Is it an EDC or mechanical version? This just rings a bell as a sign of the EDC injector having a fault - there isn't that many about and, to make it worse, AFAIK the injector is not available, only refurb of yours is the option.
Have a google on the 300TDi EDC to check it out, but I believe all or most UK 300 Autos were EDC (Australia apparently didn't have any).

Your other option if EDC is to get a manual pump and injector. You can fit them to swap to mechanical only. 

All of this is bumkin if it ain't EDC.

If not then it would suggest a fuel issue, though it's strange, the lift pump is best to have, but you can definitely run without it and probably notice no difference (I didn't), and everything else would tend to be it either works or not on these motors.

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1 hour ago, steve_a said:

Is it an EDC or mechanical version? This just rings a bell as a sign of the EDC injector having a fault - there isn't that many about and, to make it worse, AFAIK the injector is not available, only refurb of yours is the option.
Have a google on the 300TDi EDC to check it out, but I believe all or most UK 300 Autos were EDC (Australia apparently didn't have any).

Your other option if EDC is to get a manual pump and injector. You can fit them to swap to mechanical only. 

All of this is bumkin if it ain't EDC.

If not then it would suggest a fuel issue, though it's strange, the lift pump is best to have, but you can definitely run without it and probably notice no difference (I didn't), and everything else would tend to be it either works or not on these motors.

pretty sure it's not the Bosch injector, had an issue with that in the past because the plug was filthy, always got check engine lights, stalling and lots of banging because the timing was out.

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alright i pulled the intercooler out today and cleaned it up along with all the pipework. it had alittle oil but wasnt blocked and no major buildups. hoses were in good condition. the inlet manifold had alittle bit of crud inside it too, but not too much.

didnt resolve the issue.

any other ideas? 

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Have you checked for any diesel leaks. My last 300 was from 95 and not long before I sold it the pump developed a leak from the rear distributor seal. Thinking back and triggered by looking at the battery I replaced from that truck for poor start issues, I wonder if it was a bit of air in the lines after sitting.
The other thing to check might be the fuel solenoid, perhaps this isn't opening fully, restricting the flow enough to cause the revs to drop after the surplus fuel in the pump was used.

 

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  • 5 months later...

OK been procrastinating on this for 6 months haven't been able to resolve it yet. 

fully tested MAF sensor. looks to be working. 

ohms from the accelerator pot nice and smooth. appears to be OK too. 

used an electric pump to supply the injector pump from a bottle so can safely say its not the fuel lines. 

father reckons its not the tappets. 

 

any other ideas to try. leaning towards something electrical. 

if I cant fix it soon I'll probably have to sadly scrap it or sell it for parts. 

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Have you checked the low pressure/lift fuel pump?  They often fail with perished diaphragms or leaking non-return valves, and that can give the symptoms you describe.

Tappets are an easy and quick job that costs nothing, so do them, whatever the old man reckons - they should be checked routinely anyway.

I did have a flat spot on my 300Tdi after trying a vegoil/diesel mix years ago, and replacing the fuel filters and running on pure high grade diesel after using fuel system cleaners did nothing.  It needed an injection pump rebuild, and ran very well again after that.  The cam plate and followers do wear flat spots in the pumps; these Bosch units are tougher than the Lucas CAV type, but they are not indestructible.  I used DIeselBobTuning and was very pleased with the results.  The price is very reasonable.  It'd be a shame to scrap the car for something that is fixable.

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1 hour ago, Snagger said:

Have you checked the low pressure/lift fuel pump?  They often fail with perished diaphragms or leaking non-return valves, and that can give the symptoms you describe.

Tappets are an easy and quick job that costs nothing, so do them, whatever the old man reckons - they should be checked routinely anyway.

I did have a flat spot on my 300Tdi after trying a vegoil/diesel mix years ago, and replacing the fuel filters and running on pure high grade diesel after using fuel system cleaners did nothing.  It needed an injection pump rebuild, and ran very well again after that.  The cam plate and followers do wear flat spots in the pumps; these Bosch units are tougher than the Lucas CAV type, but they are not indestructible.  I used DIeselBobTuning and was very pleased with the results.  The price is very reasonable.  It'd be a shame to scrap the car for something that is fixable.

brand new lift pump.

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If it is fitted with EDC a faulty throttle position sensor will cause the engine to run at a steady fast idle, about 1500 as a "get home" feature. Pumping the pedal can cause the sensor to send some signals to the EDC, causing the engine to respond and run faster, but as soon as the signal is lost it returns to the fast idle. The usual problem is worn tracks on the sensor where the wiper runs to vary the reisitance in the circuit and tell the EDC how far the throttle pedal is depressed. Some say the sensor can be cleaned and restored, but in my experience that is only a temporary pallative.Tthe main problem will be getting a good sensor as a replacement as parts for the EDC system are hard to get. The other solution is to replace all the lot with the mechanical system fitted to manual gearbox vehicles.

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Also, if you are finding it difficult to find a replacement throttle position sensor and therefore considering the mechanical system is included looking for a 1994 or 1995MY tdi auto as they were fitted with a mechanical system.

Electronic Diesel Control came in with the 1996MY tdi auto to improve acceleration times by increasing engine power to 120bhp.

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